In order for electrical energy to be useful to the end-user, there must be a means for converting electrical energy into mechanical energy, and vice versa. Transducers are the class of devices which convert one form of energy into another. Perhaps the most important and prevalent category of transducers are those obeying Lorentz' Force Function (sometimes called the LaPlace Force), F=B X li, where F is the Force, B is the magnetic field, I is the length of current-carrying wire in the magnetic field, i is the instantaneous current in the wire, and X is a cross-product operator. The Lorentz Force Function obeys Fleming's left-hand rule for motors: an instantaneous current, i, passing through a length of wire, I, in an orthogonal magnetic field, B, will produce a force, F, orthogonal to both the current and the magnetic field.
At the core of transducers obeying Lorentz's Force Function is a magnetic motor. A magnetic motor is composed of a permanent or electro-magnet, metal components to complete a magnetic circuit, and a coil of wire, called a drive coil. The magnet and metal components are arranged in such a way that they create a narrow air-gap between north-magnetized and south-magnetized metal parts. The air gap is typically cylindrical. The coil of wire is designed to move in the magnetic gap, in proportion to the supplied current. Magnetic motors can either generate linear (also called reciprocal) or radial motion. The present invention and disclosure will focus on linear magnetic motors.
Linear magnetic motors are an integral part of many electronics and communications products including, but not limited to, sensors, scales, actuators, vibration tables, paint shakers, microphones and loudspeakers.
For most linear magnetic motors, the fundamental topology of their design has remained relatively static for decades. Due to their antiquated design topology, current, state-of-the-art, linear magnetic motors are expensive, inefficient, and variable under load. In almost every application, the wire in a magnetic motor has a significant thermal rise. In many applications, the working temperature of the wire is around 180° C. (300° F.). At 180° C., the resistivity of the wire is about double that of room temperature, meaning that half of the usable power is wasted as Joule heat, before any efficiency calculations are even made. An example of the poor efficiency of currently available linear magnetic motors is the loudspeaker, which is often only 1% efficient, meaning that most of the supplied energy is wasted as heat. As a result, consumers buy larger amplifiers, such as a 100 Watt/Channel amplifier, when they only want 1-2 Watts of acoustic power.
The end-user of a linear magnetic motor experiences these inefficiencies as added cost and degraded performance. In order to squeeze the maximum performance out of the existing linear magnetic motor technology, many engineers have resorted to using expensive, but very strong, neodymium magnets. Using expensive neodymium magnets, while burning off half of the available energy as Joule heat, adds cost upon cost. An efficient linear magnetic motor, capable of using ceramic magnets rather than neodymium magnets, could easily reduce the overall cost to the end user of transducers built with linear magnetic motors by up to 50%. Such a large amount of waste from such a ubiquitous class of devices represents a unique opportunity to reduce cost and improve performance, saving society substantial energy and resources.
In addition to cost and performance issues, current magnetic motor transducers are subject to supply interruption. As discussed, one of the few technological innovations in magnetic motors over the past three decades has been the introduction of high-power, but expensive, neodymium magnets. China controls 97% of the world's supply for neodymium, with up to 70% of the world's supply of neodymium coming from a single, open-air mine in Inner Mongolia, the massive Baiyun Obo mine. The world's supply of neodymium could be easily interrupted if that one mine experiences an earthquake, transportation disruptions, a disease epidemic, or labor unrest. Single-source commodities always pose a significant threat of disruption or manipulation, meaning that producers of linear magnetic motors are highly susceptible to a disruption at Baiyun Obo
When compared with the existing technology, a linearly interleaved magnetic motor (“LIMM”) offers substantially improved performance and a smaller package, while using ceramic, rather than neodymium, magnets. The design magnetically gangs together two or more individual magnetic motor circuits, creating at least two long, serpentine, linear air-gaps. In order to take advantage of the long, serpentine gaps, this innovation uses a flex circuit coil which is bent or folded as many as 40 times. By using a flex circuit to regulate resistance and impedance, using combinations of series and parallel traces, this technology yields an unequaled motive-force-to-mass ratio and operates with a very small thermal rise.
A loudspeaker is a transducer which converts an electric signal into sound waves. A perfect transducer is one which is linear and time-Invariant (“LTI”), has a unit impulse response in the time domain, and a frequency response which is flat and extends, in frequency, from DC to daylight. The current home theatre, automotive, and professional loudspeaker markets are dominated by electro-dynamic transducers, which follow the same basic design that Peter Jensen patented in 1927. Electro-dynamic loudspeaker transducers fall far short of an LTI response. The chief complaint about loudspeakers using electro dynamic transducers are they have significant thermal compression, wasting almost all of the electrical energy they receive; this makes them extraordinarily inefficient; as a result, they are over-sized, creating room clutter; and they have too much wiring. Additionally, when mounting such speakers to the wall, for use in a home theatre system, they are difficult to mount; modern wall-mounted or recess-mounted loudspeakers, especially soundbars, can be “beamy” or objectionably directional; they do not seal low frequency energy well; and, generally speaking, the thinner speakers tend to perform worse.